Nonoparticles formed with rigid connector compounds

ABSTRACT

The present invention relates to a novel organosilicon particle having the formula Si a O b C c H d . The particle may be coated with an organic film, preferably a rigid connector compound. The present invention also provides a method of using the organosilicon particle and/or rigid connector compound in the formation of a low-k dielectric film.

FIELD OF THE INVENTION

[0001] This invention relates to the field of interconnect wiring ofhigh-speed integrated circuit chips. More particularly, it relates tothe formation of low dielectric constant films through the use ofnanoparticles formed with rigid connector compounds.

BACKGROUND OF THE INVENTION

[0002] In order to increase the speed of microelectronic integratedcircuits, both the size of the wiring features and the spacing betweenadjacent wires must be reduced. One critical area in need of advancementin order to simultaneously reduce the size and spacing of the wiringfeatures, and maintain a high speed of signal propagation is thedielectric material used between the metal interconnects of theintegrated circuit. For example, for a given film wire resistance R, thespeed of the interconnect signal varies as 1/RC, where C is thecapacitance between wires. Using a low dielectric constant film (low-kdielectric) makes C smaller and hence increases the speed of thecircuit. Films with dielectric constants in the range of 2-3 will beneeded within 2 years for future high-speed integrated circuits.

[0003] In addition, as distances between circuit elements becomesmaller, there are increased problems due to capacitive coupling andinduced propagation delays. One way to reduce these difficulties isthrough the use of low-k dielectrics. Low-k dielectrics lower linecapacitance of the interconnects.

[0004] U.S. Pat. No. 5,801,092 to Ayers describes a method of forming adielectric film utilizing silicon dioxide nanospheres. A non-polarorganic coating surrounds the silicon dioxide nanospheres. Ayersutilizes these organic coated nanospheres to form a porous dielectricfilm. The more porous the film, the lower its dielectric constant. Thesilicon dioxide particles are made by the hydrolysis and condensationreactions of tetraethylorthosilicate, (TEOS), as the precursor molecule.The non-polar organic film used in Ayers consists of fluoroalkylsilanecompounds. The fluoroalkylsilane compounds only bind to the nanoparticleat one end and are very flexible.

[0005] One problem with the nanosphere particles in Ayers is that thecore dielectric material is made up of silicon dioxide, which has arelatively high dielectric constant of about 4. The silicon dioxide corematerial limits the reduction of the dielectric constant of the porousfilm. Another problem in Ayers is that the organic film is flexible andbinds the nanospheres at only one site. When a dielectric film is formedby these organic coated nanospheres, the flexible organic compoundscompress and the spaces between the nanospheres are reduced. The filmstructure formed is only slightly porous resulting in a higherdielectric constant film. In addition, since the organic films areflexible, variability of compression can change the porosity of thefilm, resulting in a non-reproducible dielectric constant film.

[0006] It is thus an object of the present invention to provide ananometer scale particle that has a lower dielectric constant thansilicon dioxide and can be used in the formation of a low-k dielectricfilm.

[0007] It is another object of the present invention to provide a rigidconnector compound between particles that resists compression, resultingin a more reproducible, porous and lower dielectric constant film.

[0008] It is also an object of the present invention to provide afabrication method using the novel dielectric particle and/or rigidconnector compounds to form a low-k dielectric film.

SUMMARY OF THE INVENTION

[0009] The present invention relates to a novel organosilicon particlehaving the formula Si_(a)O_(b)C_(c)H_(d). The particle may be coatedwith an organic film, preferably a rigid connector compound. The presentinvention also provides a method of using the organosilicon particleand/or rigid connector compound in the formation of a low-k dielectricfilm.

DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention relates to an organosilicon particle havingthe formula Si_(a)O_(b)C_(c)H_(d). The mole fraction of a is about 0.05to 0.5, preferably about 0.1 to 0.4, and more preferably about 0.15 to0.25. The mole fraction of b is about 0.05 to 0.5, preferably about 0.1to 0.4, and more preferably about 0.2 to 0.35. The mole fraction of c isabout 0.05 to 0.5, preferably about 0.10 to 0.5, and more preferablyabout 0.15 to 0.4. The mole fraction of d is about 0 to 0.5, preferablyabout 0.05 to 0.4, and more preferably about 0.1 to 0.4.

[0011] The particle preferably is produced on a nanometer scale, e.g., 2to 100 nm, preferably 5 to 50 nm, using thermal decomposition oforganosiloxane, organosilane, siloxane, silane or halosilane precursormolecules.

[0012] The advantage that the particle of the present invention has overprior art dielectric particles is that it is an organosilicon particle.This carbon-containing particle has a lower dielectric constant, (k ofapproximately 2.5 to 3.5), than silicon oxide particles of the priorart.

[0013] The particle is preferably coated with an organic compound. Apreferred organic compound should (1) render the particle hydrophobic toresist moisture, (2) contain a hydrolyzable site capable of bonding tothe particle (3) lower the overall dielectric constant of the particleand (4) render the particle soluble in a non-polar solvent. Examples ofsuch preferred organic compounds are alkylsilane or alkylsilylhalidecompounds such as X₃SiR where X is about a C₁ to C₄ alkoxy or a halogenand R is about a C₈ to C₃₀ alkyl.

[0014] A more preferred organic compound is one that is a rigidconnector compound. A rigid connector compound is one that is notflexible, resists compression and will not bend back against itself.Preferred examples of such rigid connector compounds are compoundshaving the formula (R¹)₃Si—(Ar)_(n)—Si(R¹)₃, wherein R¹ is about a C₁ toC₄ alkoxy or a halogen, Ar is an aromatic or substituted aromatic and nis about 1 to 6. Preferred aromatic compounds are phenyl or substitutedphenyl, naphthyl or substituted naphthyl and anthracenyl or substitutedanthracenyl. The aromatic compounds are preferably substituted withfluorine. An especially preferred rigid connector compound isbis(trimethoxysilyl) polyphenylene.

[0015] Another example of a preferred rigid connector compound is acompound having the formula (R²)₃Si-(bco)_(n)—Si (R²)₃, wherein R² isabout a C₁ to C₄ alkoxy or a halogen, bco is an bi-cyclo-octane orsubstituted bi-cyclo-octane and n is about 1 to 6. The bi-cyclo-octanecompound is preferably substituted with fluorine. Especially preferredbi-cyclo-octane compounds are 2,4-bi-cyclo-octane andperfluro-poly-2,4-bi-cyclo-octane.

[0016] It should be noted that the rigid connector compounds may containmore than 2 hydrolyzable sites capable of being bound to the particle.

[0017] The advantage of the rigid connector compounds are that they arerigid and have at least two sites that are capable of attaching to twodifferent particles. The rigid connector compounds prevent compressionand preserve the spacing between particles when the particles are usedto produce a dielectric film. This results in a more reproducible andporous dielectric film.

[0018] The aromatic or bi-cyclo-octane compounds of the presentinvention are planar compounds that have little or no bond rotation.Thus, they are rigid compounds that do not bend back against themselves.These rigid compounds prevent the binding sites from attaching to thesame particle, preserving spacing between the particles.

[0019] In an another embodiment, the rigid connector compounds of thepresent invention are attached to a core material to form ananoparticle. The core material is preferably a dielectric material. Anysuitable dielectric material may be used such as silicon dioxide,silicon nitride, silicon oxyfluoride, organosilicon, oxidizedorganosilicon, and hydrogenated oxidized organosilicon. The preferreddielectric material is the aforementioned organsilicon particle havingthe formula Si_(a)O_(b)C_(c)H_(d).

[0020] In another embodiment, the nanoparticles of the present inventionare used to form a porous body. The process for forming such a porousbody comprises the steps of providing a plurality of core particles,coating the particle with an organic compound, placing the organiccoated particle in a solvent, placing rigid connector compounds into thesolvent to displace a portion of said organic compound, and removingsaid solvent to form the porous body. Preferably, the porous body is alow-k dielectric film. A more detailed description of this process isdescribed below.

[0021] The core particle material is made with a thermolytic synthesismethod. The synthesis method begins with preheating a high-boiling pointsolvent to a temperature of about 200 to 400° C. Any suitable inert highboiling-point solvent may be used. Preferred solvents are aromaticethers and substituted aromatic ethers, high boiling point unsaturatedhydrocarbons (for example, squalene, or 2, 6, 10, 19,23-hexamethyltetracosene) and perfluoroalkenes, e.g., perfluorokerosene.The latter have the preferred formula R⁷-ph-O-ph-R⁸, where ph is phenyl,and R⁷ and R⁸ may be the same or different and selected from phenyl andabout a C₁ to C₆ alkyl. The preferred solvent in phenyl ether at atemperature of about 250° C. Preferably, a stabilizing ligand, discussedbelow, is also placed in the solvent.

[0022] Organosiloxane, organosilane, siloxane, silane and/or halosilaneprecursor compounds are placed in a syringe and rapidly injected intothe preheated solvent. Rapid thermal decomposition of the precursorcompound results and nucleation of small amorphous silicon-containingparticles occur. The particles are allowed to grow by continued heatingof the solution for about 30 minutes. The size of particle at that timeis approximately 5 nm. Shorter or longer heating times may be used forsmaller or larger particle sizes respectively.

[0023] Preferred halosilane precursor compounds have the formula R⁴SiY₃where R⁴ is about a C₁ to C₈ alkyl and Y is a halogen, preferablychlorine.

[0024] A preferred siloxane compound that may be used in the presentinvention is hydro-silsesquioxane. It has the general formulaH_(n)Si_(n)O_(3/2n) where n is about 1 to 10.

[0025] In a preferred embodiment, the precursor compounds areorganosiloxane precursor compounds. In the present invention,organosiloxane compounds are straight, branched or cyclic compounds thatcomprise at least silicon, oxygen and carbon. Preferred organosiloxanecompounds are silsesquioxanes and cyclo-siloxanes.

[0026] Examples of silsesquioxanes are incompletely condensed and fullycondensed silsesquioxanes. Incompletely condensed silsesquioxanes havethe general formula (R⁵SiO_(3/4))_(n) (H₂O)_(3n/2) where R⁵ is about aC₁ to C₈ alkyl and n is about 1 to 10. Incompletely condensedsilsesquioxanes are formed when compounds of the formula R⁵Si(OH)₃ areheated and water is removed.

[0027] Fully condensed silsesquioxanes are made by removing water fromthe partially condensed silsesquioxanes. They have the general formula(R⁵SiO_(3/2))_(n). Commercially available examples of fully condensedsilsesquioxanes that may be used in the present invention are when n is6, 8 and 10.

[0028] Cyclo-siloxanes may also be used as precursor compounds of thepresent invention. The preferred cyclo-siloxanes have the generalformula R⁶ _(n)H_(n)(SiO)_(n) and R⁶ _(2n)(SiO)_(n) where R⁶ is about aC₁ to C₈ alkyl and n is about 1 to 10.

[0029] Another preferred organosiloxane has the general formulaCH₃O(SiO(CH₃O)₂)_(n)OCH₃ where n is about 1 to 10.

[0030] Examples of especially preferred organosiloxane and organosilanecompounds are tetraethylorthosilicate, (TEOS), tetramethylsilane (TMS),tetramethylcyclotetrasiloxane (TMCTS), tetraethylcyclotetrasiloxane,(TECTS), cyclotetrasiloxane, cyclopentasiloxane,pentamethylpentasiloxane and mixtures thereof.

[0031] These compounds are used to prepare the preferred organosiliconparticles of the present invention. For example, a mixture ofTEOS:TMS:TMCTS in a ratio of 1:3:2 will result in an amorphous particlecontaining Si:O:C in a ratio of about 1:1:2.3. Particles with higher orlower carbon content may prepared by varying the ratio and carboncontent of precursor compounds. For example, TECTS may be used insteadof TMCTS in the above mixture to increase the carbon content of theresulting particle.

[0032] After the particles are grown to their desired size, the reactionis cooled to a convenient low temperature so that the particles stopgrowing. The temperature should be less than about 150° C., preferablyless than 100° C., and more preferably about 60° C. A stabilizing ligandis then added. The stabilizing ligand is an organic compound that coatsthe particles. Preferably, the stabilizing ligand has the formula X₃SiRwhere X is about a C₁ to C₄ alkoxy or a halogen and R is about a C₈ toC₃₀ alkyl. Preferably, R is about a C₁₂ to C₂₄ alkyl and more preferablya C₁₆ to C₂₀ alkyl. When the stabilizing ligands are added, they bind tothe particle surface. Optionally, the particles are annealed by raisingthe solution temperature to 300 to 350° C. for a desired time.

[0033] The organic-coated particles may now be precipitated using apolar solvent such as ethanol. Optionally, the particles may be isolatedand purified by size selective precipitation to yield a nearlymono-disperse fraction of particles.

[0034] A first method of size selective precipitation involves thegradual addition of a polar solvent. A selective amount of polar solventis added to the organic coated particle mixture. In this process, thelargest size organic coated particles are precipitated first and can beisolated by centrifugation or filtration. Subsequent addition of thepolar solvent to the organic-coated particle mixture will precipitateparticles of slightly smaller sizes. This process can be continued toprepare a distribution of particles sizes. To achieve a nearlymono-disperse particle size, any of the isolated fractions can bere-dispersed in a non polar solvent and subjected to more cycles of sizeselective precipitation to achieve an arbitrary, narrow, nearlymono-disperse size distribution.

[0035] A second method of size selective precipitation consists ofdissolving the particle in a mixture of two solvents: one more volatileand non-polar (i.e., pentane) and one less volatile and polar. Slowevaporation of the solvent mixture reduces the amount of the morevolatile non-polar solvent resulting in the precipitation of the largestsize organic coated particle. Precipitation of slightly smallerparticles can be performed in stages by further evaporation to achieve adistribution of particle sizes. The above process may be repeated toachieve a nearly mono-disperse particle size distribution.

[0036] The size selective particles are then re-dispersed in a non-polarsolvent at a temperature of about 60° C. The rigid connector compound ofthe present invention is then added to the solution. The solution isstirred and the rigid connector compounds replace some of the organicstabilizer ligands that are bound to the particles. This step is calledligand exchange. After stirring for about 30 minutes, the organicstabilizer ligands and rigid connector compounds reach equilibriumconcentration on the surface of the particles. As discussed above, therigid connector compounds contain at least two sites that are capable ofbinding on the particles. Their rigidity does not allow them to bend sothat two sites will not bind to one particle.

[0037] The amount of rigid connector compounds attached to the particlesmay be increased by re-dispersing the organically coated particles in anon-polar solvent and repeating the ligand exchange step.

[0038] It should be noted that in a preferred embodiment, the length ofthe organic stabilizer ligand is longer than the rigid connectorcompound. This prevents the rigid connector compound from binding orcross-linking with two particles at this step of the process. If theparticles become cross-linked, gel particles or precipitates form suchthat the particles can not be readily coated on a substrate.

[0039] The organically coated particles are then coated on a substrateby any suitable method such as spin coating, dip coating, doctorblading, or spray coating. The thickness of the coating will typicallyrange from about 0.1 to 2 um, preferably about 0.1 to 1 um.

[0040] The organically coated particles are then cross-linked such thatthe rigid connector compounds are attached to at least two particles. Toperform the cross-linking, the substrate containing the organicallycoated particles is placed in an oven, preferably a vacuum oven. Thesubstrate is heated to a temperature of about 250° C. to 300° C. At thistemperature, the organic stabilizer ligands are removed by desorptionand/or decomposition from the particles and are removed along with thesolvent. The unattached sites of the rigid connector compounds nowattach to a neighboring particle and cross-links are formed. Thesubstrate is then heated to a higher temperature of about 300° C. to350° C., which removes any rigid connector compounds that are notcross-linked to two particles. The substrate now contains a porous bodyor film that is suitable to be used as a dielectric film.

[0041] Optionally, the porous body may be coated with a hydrophobiccompound such as hexaphenyldisilane or hexamethyldisilazane (HMDS) tomaintain moisture resistance. In this step, the substrate is placed in avacuum oven at about 150° C. The oven is evacuated, and the sample isleft at 150° C. for about 10 minutes, The oven is then filled with avapor of hexamethyldisilazane or hexaphenyldisilazane entrained in aninert gas (nitrogen or argon) with the substrate remaining at 150° C.temperature. After about 20 minutes, the oven is cooled to roomtemperature and evacuated, and is then held for about 10 minutes. Thisprocedure coats the interior pores with a water repellent (hydrophobic)coating, so the porous body will not absorb moisture and is renderedinert. The oven is then filled with a pure inert gas, and the substrateis removed.

[0042] It should be noted that the foregoing description is onlyillustrative of the invention. Various alternatives and modificationscan be devised by those skilled in the art without departing from thepresent invention.

1. A particle comprising a compound of the formulaSi_(a)O_(b)C_(c)H_(d), wherein the mole fraction of a is about 0.05 to0.5, the mole fraction of b is about 0.05 to 0.5, the mole fraction of cis about 0.05 to 0.5, and the mole fraction of d is about 0 to 0.5. 2.The particle of claim 1 wherein said particle is coated with at leastone organic compound.
 3. The particle of claim 2, wherein said organiccompound is a rigid connector compound.
 4. The particle of claim 3wherein said rigid connector compound has the formula(R¹)₃Si—(Ar)_(n)—Si(R¹)₃, wherein R¹ is about a C₁ to C₄ alkoxy or ahalogen, Ar is an aromatic or substituted aromatic and n is about 1 to6.
 5. The particle of claim 4 wherein said aromatic is selected from thegroup consisting of a phenyl or substituted phenyl, naphthyl orsubstituted naphthyl and anthracenyl or substituted anthracenyl.
 6. Theparticle of claim 4 wherein said aromatic is substituted with fluorine.7. The particle of claim 4 wherein said rigid connector compound isbis(trimethoxysilyl) polyphenylene.
 8. The particle of claim 3 whereinsaid rigid connector compound has the formula (R²)₃Si-(bco)_(n)—Si(R²)₃,wherein R² is about a C₁ to C₄ alkoxy or a halogen, bco is anbi-cyclo-octane or substituted bi-cyclo-octane and n is about 1 to
 6. 9.The particle of claim 8 wherein said bi-cyclo-octane is2,4-bi-cyclo-octane.
 10. The particle of claim 8 wherein saidbi-cyclo-octane is substituted with fluorine.
 11. The particle of claim1 wherein said particle is made from one or more precursor compoundsselected from the group consisting of organosiloxane, organosilane,siloxane, silane, halosilane.
 12. The particle of claim 11 wherein saidone or more precursor compounds are selected from the group consistingof tetraethylorthosilicate, tetramethylsilane,tetramethylcyclotetrasiloxane, tetraethylcyclotetrasiloxane,cyclotetrasiloxane, cyclopentasiloxane, and pentamethylpentasiloxane.13. A film comprising a plurality of the particles of claim
 1. 14. Ananoparticle comprising a core material and a rigid connector compound.15. The nanoparticle of claim 14 wherein said core material is adielectric material.
 16. The nanoparticle of claim 15, wherein the corematerial is selected from the group consisting of silicon dioxide,silicon nitride, silicon oxyfluoride, organosilicon compounds, oxidizedorganosilicon and hydrogenated oxidized organosilicon.
 17. Thenanoparticle of claim 15 wherein said rigid connector compound has theformula (R¹)₃Si—(Ar)_(n)—Si(R¹)₃, wherein R¹ is about a C₁ to C₄ alkoxyor a halogen, Ar is an aromatic or substituted aromatic and n is about 1to
 6. 18. The nanoparticle of claim 17 wherein said aromatic is selectedfrom the group consisting of a phenyl or substituted phenyl, naphthyl orsubstituted naphthyl and anthracenyl or substituted anthracenyl.
 19. Thenanoparticle of claim 17 wherein said aromatic is substituted withfluorine.
 20. The nanoparticle of claim 18 wherein said rigid connectorcompound is bis(trimethoxysilyl) polyphenylene.
 21. The nanoparticle ofclaim 15 wherein said rigid connector compound has the formula(R²)₃—Si-(bco)_(n)—Si(R²)₃, wherein R² is C₁ to C₄ alkoxy or a halogen,bco is an bi-cyclo-octane or substituted bi-cyclo-octane and n is about1 to
 6. 22. The nanoparticle of claim 21 wherein said bi-cyclo-octane is2,4-bi-cyclo-octane.
 23. The nanoparticle of claim 21 wherein saidbi-cyclo-octane is substituted with fluorine.
 24. A dielectric filmcomprising a plurality of the nanoparticles of claim
 15. 25. Adielectric film comprising a plurality of the nanoparticles of claim 15,wherein said nanoparticles are bounded together by said rigid connectorcompound.
 26. The dielectric film of claim 25 wherein said film isfurther coated with a hydrophobic compound.
 27. A process for forming aporous body comprising the steps of: (a) providing a plurality of coreparticles; (b) coating said particles with an organic compound; (c)placing said organic coated particles in a solvent; (d) placing a rigidconnector compound into said solvent to displace a portion of saidorganic compound; and (e) removing said solvent to form said porousbody.
 28. The process of claim 27 wherein said rigid connector compoundhas the formula (R¹)₃Si—(Ar)_(n)—Si(R¹)₃, wherein R¹ is about a C₁ to C₄alkoxy or a halogen, Ar is an aromatic or substituted aromatic and n isabout 1 to
 6. 29. The process of claim 27 wherein said rigid connectorcompound has the formula (R²)₃Si-(bco)_(n)—Si(R²)₃, wherein R² is abouta C₁ to C₄ alkoxy or a halogen, bco is an bi-cyclo-octane or substitutedbi-cyclo-octane and n is about 1 to
 6. 30. The process of claim 27wherein said core material has the formula Si_(a)O_(b)C_(c)H_(d),wherein the mole fraction of a is about 0.05 to 0.5, the mole fractionof b is about 0.05 to 0.5, the mole fraction of c is about 0.05 to 0.5and the mole fraction of d is about 0 to 0.5.
 31. The process of claim27 wherein said rigid connector compound contains fluorine.
 32. Theprocess of claim 27 wherein said porous body is further coated with ahydrophobic compound.
 33. The process of claim 27 wherein the length ofsaid organic compound is longer than said rigid connector compound.